The use of synthetic fibers for the production of surgical barrier fabrics is well known. Conventionally, barrier fabrics made from these fibers are treated for repellency to water, blood, body fluids, prep solutions, isopropyl alcohol solutions, and other liquids encountered in medical or surgical practice. In addition to being resistant to wetting and penetration by liquids, barrier fabrics may also be treated for antistatic performance.
A guide for the performance of barrier fabrics is contained in the Association for the Advancement of Medical Instrumentation, Technical Information Report Number 11: Selection of Gowns and Drapes in Health Care Facilities, 1994a, which is incorporated herein by reference in its entirety. This guide discusses the importance of liquid repellency and static control for barrier fabrics.
Historically, barrier fabrics used in surgical practice have been cotton or cellulose based. Hospital “linens” conventionally have been based on cotton sheeting or canvas, having an aqueous dispersion with a blend of fluorochemical repellents, wax based repellents and salt type antistats.
Upon the introduction of nonwoven surgical barrier fabrics in the late 1970's, a blend of woodpulp and polyester fibers were spunlaced into fabrics that were finished in a similar way to hospital linens. In these nonwoven barrier fabrics, the woodpulp component conventionally provides the barrier properties and the polyester provides strength.
Around 1980, Kimberly Clark introduced a new type of nonwoven fabric that is commonly known as SMS (spunbond-meltblown-spunbond). SMS fabric is a thermal bonded composite of three nonwoven layers; a top layer of spunbond, a middle layer of meltblown fiber, and a bottom layer of spunbond. SMS fabrics conventionally are made from polypropylene; however, they can be produced from most polymers that are melt spinnable.
The finishing of barrier fabrics with liquid repellent chemistry is well known. Fabrics made from cotton and treated with Quarpel® brand finishes have been extensively used for rainwear, and medical barrier fabrics. Quarpel® brand finishes are water based dispersions of fluorochemical repellent with a stearylol melamine-wax repellent extender. The use of fluorochemical repellents have been used extensively to finish nonwovens and other textiles for a variety of end uses.
Fluorochemical treatment of barrier fabrics, such as SMS fabrics, is described in U.S. Pat. No. 5,441,056 to Weber et al., and U.S. Pat. No. 5,178,932 to Perkins et al., each of which is incorporated herein by reference in its entirety. Conventionally, fluorochemical finishing combines a fluorochemical repellent, a wetting agent, and an antistat in a treating bath.
Fluorochemical treatment is advantageous over silicone or wax type repellents in that the surface energy of the fiber is reduced to a point where isopropanol solutions and oils, commonly encountered in medical use, are repelled. Antistats conventionally are added to improve comfort and reduce the likelihood of an electrostatic spark in an atmosphere of enriched oxygen, or flammable vapor.
Fluorochemical treatments have been dispersed into molten polymer used to spin fiber. For example, see U.S. Pat. No. 5,145,727 to Potts et al., U.S. Pat. No. 5,149,576 to Potts et al., U.S. Pat. No. 5,178,931 to Perkins et al., U.S. Pat. No. 5,178,932 to Perkins et al., and U.S. Pat. No. 6,297,304 to Raiford et al., each of which is incorporated herein by reference in its entirety. The incorporation of fluorochemicals into the melt can be problematic due to decomposition at high spinning temperatures, loss of material to vaporization, and inefficiency of material not at the surface of the fiber. Additionally, the use of a melt antistat may further complicate this process.
Conventional water-based finishing systems contain a fluorochemical dispersion and a wetting agent, and may also contain an antistat. Water-based systems may be efficient in the amount of chemistry required to achieve repellent properties in barrier fabrics; however, there are some significant limitations. For example:
1) Water-based systems may require a surfactant or co-solvent. A surfactant can destabilize the fluorochemical, cause rewetting, and foaming. The choice of surfactant is very limited when compatibility with the fluorochemical and rewetting are considered. The surface tension required to wet polypropylene based materials is a surface tension below 32 dynes/centimeter. This is difficult to achieve and may result in uneven wetting of the fibers, especially the micro and nano denier types. Additionally, when very low porosity materials are treated, it may be difficult if not impossible to penetrate into the center of the barrier layers.
2) Water-based systems may require heat to dry and cure the fluorochemical. The exposure to high levels of heat may stiffen most fabrics, may result in tensile, burst, or tear strength loss, may drive off the antistat resulting in static control failure, and may yellow many fibers.
3) Water-based systems typically operate at only 1–5% solids. This may result in excessive use of energy to evaporate and drive off the water from the fabric. This may require more energy as the fiber diameter is reduced and surface area increases.
4) Water-based fluorochemical repellents used on naturally hydrophobic fibers tend to leave much of the fiber surfaces untreated. The untreated fibers may serve as a conduit for penetration and wicking of contaminants. Additionally, if an antistat is used in conjunction with a fluorochemical repellent, the antistat may migrate to the untreated fibers as it is repelled by the fluorochemical. The antistat is generally a higher surface energy material and may render sections of the barrier material non-repellent by raising the surface energy of the fibers and allowing them to wet by aqueous contaminants such as blood.
5) Fluorochemical dispersions generally have a cationic charge. Charged fluorochemical particles are preferentially attracted to negatively charged fiber surfaces and may deplete the finishing bath, and also may result in uneven deposition on the fiber. The uneven deposition may lead to untreated or poorly treated sections of the fiber and they may be sources of barrier failure, or conduits for antistat migration.